This invention relates generally to gas turbine engines and more particularly to engine case inlet and intake duct seals. In gas turbine powered aircraft, especially military aircraft, there are several advantages in placing the gas turbine engine within the aft portion of the aircraft fuselage. For example, there is less drag as compared with aircraft having wing suspended engine nacelles. In twin engine aircraft, there is less asymmetric yaw produced when one engine fails, as the engines are closer to the center axis of the aircraft. It is also advantageous in stealth aircraft to reduce the radar signature produced by the engine profile. Thus, there are many advantageous in having the engine completely integrated within the aircraft fuselage.
There are, however, disadvantages associated with internal engine placement. Foremost, it is necessary to route air through the fuselage from the front of the aircraft to the engine inlet in order to provide oxygen required for combustion. Problems also arise with overheating of the engine bay since the engine is encapsulated within the fuselage where heat is not readily dissipated. Engine components and other aircraft components located inside the engine bay can overheat and become damaged if the engine bay reaches too high of a temperature. Also, since the engine is in more intimate contact with the fuselage, vibration throughout the aircraft is more pronounced.
In aircraft having internal mounted engines an air intake duct is typically integrated with the aircraft fuselage and connects the front of the aircraft with the engine case inlet in order to provide oxygen to the engines for supporting combustion. A portion of this inlet air can be diverted from flowing into the engine case, to flowing around the exterior of the engine case in order to cool the engine bay. This can be accomplished by using a plenum system in the intake duct seal that permits a pressure differential across the seal to mechanically disengage a compression seal between the intake duct and engine case inlet. A small amount of inlet air then passes through and cools the engine bay. However, high cycle fatigue produced by engine vibration and acoustics can cause cracks to form in the compression seal, which leads to failure of the compression seal.